1. The Field of the Invention
The present invention relates to fiber optic sensors, particularly to sensors substantially not affected by very strong electromagnetic fields, and in the presence of Radio Frequency interferences produced by power electric generators, high voltage power utilities, electrical transformers and similar equipment.
2. The Relevant Technology
Fiber optic sensors such as accelerometers and pressure, temperature, displacement sensors, etc. are known to use light energy and optical fibers to sense physical parameters and transform measured signals representative of the physical parameters into modulation of light energy. Examples of such sensors are disclosed in U.S. Pat. No. 5,771,091; US 2009/0013112 and US 2007/0247613 in which the sensor includes two optical fibers. One fiber channels light energy from a light source to a sensing object that moves under the influence of sound or vibration/acceleration. The second fiber channels the reflected light energy modulated by these movements to a light detector that produces an electrical sensor output signal.
The disadvantages of such sensors are complexity of their construction and the need for highly qualified personnel for their assembly as well as the need for two optical fibers that further complicate the mounting of the sensor when measuring acceleration of objects. The sensor disclosed in US 2007/0247613 would appear to have very low resolution due to the large distance of light travel between the ends of both optical fibers in a reflecting body constituted by a two-face mirror. This large distance of light travelled also prevents such an accelerometer from detecting high frequencies since the resolution is very poor for high frequency detection. Another drawback of this sensor is that it can measure the acceleration in only one direction perpendicular to the plane of both optical fibers. To measure acceleration in other direction there is a need to use another sensor whose optical fibers are arranged in another orientation. The need for two optical fibers results in high cost both for the sensor itself and for its assembly as well as installation of the sensor on objects owing to the provision of two optical fibers. All of this is a source of high production costs of such sensor as well the high cost of its manufacture.